a laser oscillation optical system configured to produce a pulsed laser light;

a condensing optical element configured to condense the pulsed laser light into a combustion chamber;

a housing internally containing the condensing optical element; and

an optical window provided distally with respect to the condensing optical element in the housing and configured to transmit the pulsed laser light, wherein

the pulsed laser light is shaped as a ring around an optical axis at least at a light passage position in the optical window,

the laser oscillation optical system includes an axicon lens configured to transform incident light into outgoing light shaped as the ring around the optical axis,

the laser oscillation optical system includes an excitation light source configured to generate excitation light, the axicon lens configured to receive and transform the excitation light into the ring-shaped outgoing light, a collimator lens configured to transform the ring-shaped outgoing light into collimated light parallel with the optical axis, and a laser resonator configured to be excited by the excitation light received as the collimated light to emit the pulsed laser light, and

the laser resonator includes an inert medium formed in an area including the optical axis and a cylindrical medium formed around an outer periphery of the inert medium, and a refractive index of the cylindrical medium is higher than a refractive index of the inert medium, and the pulsed laser light undergoes resonance in the cylindrical medium.